Crosslinking agent for crosslinkable silicone composition with low platinum content based on hydrogenated silicone oil comprising si-h units in chain end and in the chain

ABSTRACT

The invention concerns crosslinkable silicone compositions, useful for forming water-repellent and release coating for flexible heat-sensitive support. Said compositions comprise crosslinking polyorganosiloxanes (POS) bearing ≡Si—H units and unsaturated POS, for example ≡Si-Vi vinyl-containing POS, capable of reacting with the crosslinking agent by polyaddition, in the presence of platinum to form a release crosslinked coat on the flexible support. The invention aims at instantaneously enabling low platinum content crosslinking of such silicone compositions, coated at high speed. Therefor, the invention provides for the use of particular crosslinking agents consisting of hydrogenated POS comprising at least three hydrogen atoms bound to the silicon located at chain end and in the chain. The invention also concerns solvent-free or emulsion-type silicone compositions comprising the ≡Si-Vi POS (I.1), the crosslinking agent ≡Sl-H POS (l.2) and the platinum catalyst among others. The invention is useful for coating flexible supports, for example made of Lissé BEKK&gt;1000 paper.

The field of the invention is that of crosslinkable or crosslinkedsilicone compositions capable of being used in particular to form awater-repellent and release coating or film on a fibrous or nonfibroussupport, for example made of paper or the like, or alternatively made ofnatural or synthetic polymers.

More specifically, the invention relates to silicone compositions of thetype of those comprising:

-   -   functionalized polyorganosiloxanes (POS) carrying, on the same        molecule or not, Si—H and Si—IE units with IE representing a        group comprising at least one ethylenic, preferably vinyl,        unsaturation; the Si—H units being capable of reacting with the        Si—IE units by polyaddition;    -   an appropriate metal catalyst, preferably a platinum catalyst;    -   optionally at least one adhesion-adjusting system, for example        based on silicone resin comprising Q (SiO_(4/2)) and/or T        (RSiO_(3/2)) siloxyl units;    -   optionally other additives (fillers, accelerators, inhibitors,        pigments, surfractants, and the like).

The invention also relates to the preparation of silicone compositionsof this type.

The invention also relates to the processes for the manufacture ofarticles made of crosslinked silicone, in particular coatings, e.g.water-repellent and/or release coatings, for fibrous or nonfibrousflexible supports (paper or polymer film), from the compositionstargeted above.

For example, these liquid silicone compositions (with/without solvent orin aqueous emulsion) are applied to support films in industrial coatingdevices comprising rolls operating at a very high speed (for example 600m/min). It is obvious that, in these very high-speed coating proceduresthe viscosity of the liquid silicone coating composition must beprecisely adapted to the coating operating conditions.

The liquid silicone coating compositions of more particular interest inthe context of the invention are solvent-free.

According to an alternative form, the silicone phase of these liquidsilicone coating compositions can be diluted in a solvent. According toanother more advantageous alternative form, in particular for reasons ofhealth and safety, the liquid silicone composition is an aqueousdispersion/emulsion.

In practice, the degree of deposition of release silicone is between 0.1and 2 g/m², preferably 0.3 and 1 g/m², which corresponds to thicknessesof the order of a micrometer.

Once applied to the flexible support, the silicone compositioncrosslinks to form a firm, release and/or water-repellent, coating madeof silicone (e.g. elastomer).

In the case of solvent-free liquid silicone systems which crosslink bypolyaddition [Si—H/Si-alkenyl-(Vi)-], crosslinking is carried out underthermal activation.

In view of the very high-speed industrial coating rates, the kinetics ofcrosslinking have to be instantaneous and the crosslinking has to becorrect, that is to say that the release silicone films have to besufficiently crosslinked to be able to fulfill as best as possible theirrelease role and to possess the desirable mechanical qualities. Theassessment of the quality of the crosslinking of the release siliconefilm can be carried out in particular through quantitative determinationof the uncrosslinked extractable compounds, the amount of which must beas small as possible.

The ability to release of the free outer face of the silicone coating isexpressed through the detachment force, which has to be weak andcontrolled, for the element intended to be positioned on the supportcoated by the release silicone film. Conventionally, this element can bethe adhesive face of a label or of a tape of the same kind.

Thus, in addition to this weak and controlled ability to release, theadhesion of the silicone coating to its support has to be very high.This property of adhesion is assessed, for example, using the rub offtrade test, which consists in rubbing the surface of the coating with afinger and then measuring the number of successive passes which resultin damage to the coating.

It is also important for these silicone coating compositions which canbe crosslinked by hydrosilylation, e.g. ≡Si—H/≡Si—Vi, to have a lifetimeat ambient temperature which is as long as possible, when they are inthe form of a coating bath in industrial coating devices.

The flexible supports coated with a release silicone film can be, forexample:

-   -   an adhesive tape, the inner face of which is coated with a layer        of pressure-sensitive adhesive and the outer face of which        comprises the release silicone coating;    -   or a paper or a polymer film for protecting the adhesive face of        a self-adhesive element or pressure-sensitive adhesive;    -   or a polymer film of the Poly(Vinyl Chloride) (PVC),        PolyPropylene, PolyEthylene or PolyEthylene Terephthalate) type.

Another major constraint in these silicone coating compositions whichcan be crosslinked by hydrosilylation, e.g. ≡Si—H/≡Si-Vi, in thepresence of platinum is specifically related to their platinum content.This is because platinum is, because of its cost, a dominating elementin the cost price of a polyaddition system, in particular for therelease and/or water repellent silicone coating application for flexiblesupports (paper or polymer film).

In point of fact, if, for reasons of economy, the level of platinum isreduced to a level of less than 100 ppm, indeed even of less than 80ppm, in the composition, it is then no longer possible to obtain fullycrosslinked release and/or water-repellent silicone coatings. The use ofcrosslinking agents of the type of those comprising siloxyl units:dimethylhydrosiloxyl (M′), methylhydrosiloxyl (D′), dimethylsiloxyl (D)and trimethylsiloxyl (M), for liquid silicone compositions which can becrosslinked by polyaddition (≡Si—H/Si-Vinyl), to form release coatingson flexible supports (coated or uncoated paper, polymer films, and thelike), is generally already disclosed.

This is thus the case in Patent Application EP A-0 523 660, whichdiscloses silicone compositions which can be crosslinked in a fewseconds at temperatures below 100° C. and which comprise network(nonlinear) ≡Si-Vi POS resins and ≡Si—H POS crosslinking agents of MD′,MDM′ type. It is not at all shown in this document that the crosslinkingof the silicone films obtained is correct for low levels of platinum(less than 100 ppm). The level of extractables is not measured in theexamples. The only level of platinum mentioned in the latter is 100 ppm.

EP-A-0 523 660 does not relate to a specific ≡Si—H POS crosslinkingagent which confers advantageous properties on the crosslinked coatingin terms of reduced level of extractables and of duration of stabilityof the bath of liquid silicone coating composition, in particular.

In this context, an essential object of the present invention is toprovide a novel use of specific ≡Si—H POSs as crosslinking agents inliquid silicone coating compositions which can be crosslinkedinstantaneously under thermal activation, with a low level of metalcatalyst (e.g. Pt), to give a release and/or water-repellent coating fora flexible support, while resulting in crosslinked silicone coatings ofvery good quality characterized by reduced levels of extractables whichfurthermore have excellent attachment properties, in particular tosmooth supports, for example made of glassine paper with a Bekksmoothness of greater than 1000.

Another essential object of the invention is to provide a novel use ofspecific ≡Si—H POSs as crosslinking agents in liquid silicone coatingcompositions which can be crosslinked instantaneously under thermalactivation, with a low level of metal catalyst (e.g. Pt), to give arelease and/or water-repellent coating for a flexible support, whileexhibiting long bath lifetimes at ambient temperature.

Another essential object of the invention is to provide a novel use ofspecific ≡Si—H POSs as crosslinking agents in liquid silicone coatingcompositions which can be crosslinked instantaneously under thermalactivation, with a low level of metal catalyst (e.g. Pt), to give arelease and/or water-repellent coating for a flexible support and whichresult in correctly crosslinked silicone coatings having entirelysatisfactory release properties.

Another essential object of the invention is to provide a novel use ofspecific ≡Si—H POSs as crosslinking agents in liquid silicone coatingcompositions which can be crosslinked instantaneously under thermalactivation, with a low level of metal catalyst (e.g. Pt), to give arelease and/or water-repellent coating for a flexible support and whichresult in correctly crosslinked silicone coatings having entirelysatisfactory attachment properties.

Another essential object of the invention is to provide a novel use ofspecific ≡Si—H POSs as crosslinking agents in liquid silicone coatingcompositions which can be crosslinked instantaneously under thermalactivation, with a low level of metal catalyst (e.g. Pt), to give arelease and/or water-repellent coating for a flexible support and whichresult in correctly crosslinked silicone coatings having entirelysatisfactory mechanical properties.

Another essential object of the invention is to provide a novel use ofspecific ≡Si—H POSs as crosslinking agents in liquid silicone coatingcompositions which can be crosslinked instantaneously under thermalactivation, with a low level of metal catalyst (e.g. Pt), to give arelease and/or water-repellent coating for a flexible support and whichresult in correctly crosslinked silicone coatings having entirelysatisfactory water-repelling properties.

Another essential object of the invention is to provide a novel liquidsilicone coating composition which can be crosslinked instantaneouslyunder thermal activation, with a low level of metal catalyst (e.g. Pt),to give a release and/or water-repellent coating for a flexible support,this composition additionally having the same qualities as thosementioned above for the use.

Another essential object of the invention is to provide a novel liquidsilicone coating composition which can be crosslinked instantaneouslyunder thermal activation, with a low level of metal catalyst (e.g. Pt),to give a release and/or water-repellent coating for a flexible support,this composition additionally being easy to prepare and economical.

Another essential object of the invention is to provide a process forthe production under thermal activation, with a low level of metalcatalyst (e.g. Pt), of release and/or water-repellent crosslinkedsilicone coatings on flexible supports.

These objects, among others, are achieved by the present invention,which relates first to a novel use as crosslinking agent (I.2), in asilicone composition capable of crosslinking by polyaddition to form awater-repellent and release coating for a fibrous or nonfibrous support,

-   -   of at least one silicone oil comprising at least one        hydrogenated (preferably linear) PolyOrganoSiloxane (POS)        exhibiting, per molecule, at least three hydrogen atoms bonded        to silicon atoms, and preferably having the following mean        formula:        M_(α)M′_(β)D_(γ)D′_(δ)    -   with        -   M=(R¹)₃SiO_(1/2)        -   M′=H_(a)(R¹)_(b)SiO_(1/2), a+b=3, a=1, 2 or 3,        -   b=0 to 3        -   D=(R²)₂SiO_(2/2)        -   D′=HR³SiO_(2/2)        -   0≦α≦2        -   0<β≦2        -   0<γ        -   0<δ    -   and with:        -   0<γ/δ≦0.4,        -   20≦(β/δ)×1000≦60,    -   the POS or POSs of higher viscosity of said composition having a        dynamic viscosity η at 25° C. of less than or equal to 1500        mPa·s;    -   the level of metal catalyst being less than or equal to 80 ppm,        preferably less than or equal to 65 ppm and more preferably        still of between 30 and 55 ppm.

The use according to the invention of carefully selected ≡Si—H POScrosslinking agents makes it possible to produce, with low levels ofplatinum, therefore economically, release coatings on flexible supports.By virtue of the invention, correct crosslinking of the coating isprovided at levels of platinum of less than 80 ppm, preferably of theorder of 60 ppm and ideally of 40 ppm, for example, this being the caseunder industrial coating conditions, e.g. at a temperature of 150° C.

Furthermore, these novel ≡Si—H POS crosslinking agents do not modify theTheological behavior of the silicone composition, so that it isperfectly capable of being coated on any support and in particular onany flexible support.

This final property is all the more advantageous as, in the context ofthe invention, the silicone coating compositions can advantageously be“solvent-free”. This means that they are devoid of solvent and inparticular of organic solvent. The advantages which this providesregarding health and safety are easily understood.

The performance achieved by virtue of the invention in terms of qualityof the crosslinking by polyaddition: reactivity/level ofcrosslinking/kinetics, are entirely advantageous, as testified theretoby the low levels of extractables obtained, as regards the reactivityand the level of crosslinking.

It is the same as regards the attachment to supports, in particular tovery smooth flexible supports (for example made of paper).

Thus, the use according to the invention is distinguished in that thesilicone composition employed can be converted according to a specificmethodology M to a crosslinked silicone elastomer coating on a supportmade of paper with a Bekk smoothness of greater than 1000, said coatingbeing characterized by a positive attachment in a specific test T.

The methodology M and the test T are defined below in the examples.

The formula of the ≡Si—H POS crosslinking agent (I.2) indicated above isan overall formula which covers:

-   -   -a- the cases where the ≡Si—H POS crosslinking agent (I.2)        comprises the MM′DD′ units on the same (preferably linear)        POSmolecule, it being possible for the crosslinking agent to        comprise one or more different MM′DD′ molecules,    -   -b- the cases where the ≡Si—H POS crosslinking agent (I.2) is        formed by a mixture of (preferably linear) POS molecules each        carrying a portion of the MM′DD′ units,    -   -c- the cases where the ≡Si—H POS crosslinking agent (I.2) is        formed by a mixture of (preferably linear) ≡Si—H POS        crosslinking agents (I.2) of -a- and -b- types as described        above.

Mention may be made, as examples of ≡Si—H POS crosslinking agents (I.2)of -b- type, of mixtures of ≡Si—H POS comprising M and D′ units and ofPOS comprising M, D and D′ units, or mixtures of ≡Si—H POS (I.2)comprising M and D units and of POS comprising M′, D and D′ units, ormixtures of =Si—H POS (I.2) comprising M and D′ units and of POScomprising M and D units, or mixtures of ≡Si—H POS (I.2) comprising M′and D′ units and of POS comprising M and D units.

The invention also covers alternative forms in which the crosslinkingagent (I.2) comprises hydrogenated POSs carrying T, RSiO_(3/2), or Q,SiO_(4/2), units. It can, for example, be≡Si—H POS (I.2) with astructure M′DD′QM′.

As emerges from the -b- cases, the crosslinking agent comprising M′ andD′ units according to the invention can also comprise standard ≡Si—H POScrosslinking agents (I.2) not having M′ functional groups.

Preferably, the silicone composition involved in the use according tothe invention is composed of ≡Si—H POS (I.2) and of ≡Si-alkenyl (e.g.Vi) POS (I.1) with a linear, optionally branched, structure, with theexclusion of ≡Si—H POS (I.2) and of ≡Si-alkenyl (e.g. Vi) POS (I.1)having a network crosslinked structure.

According to an advantageous form of the invention, the support intendedto be coated is made of a heat-sensitive material, preferably a flexiblematerial, and more preferably still is chosen from flexible supportsmade of paper, board or the like, flexible supports composed of theadhesive face of a label or of a tape of the same kind, woven ornonwoven fibrous flexible supports, flexible supports comprisingpolyethylene and/or polypropylene and/or polyester and/or poly(vinylchloride), and/or thermally printable flexible supports.

According to the invention, for the crosslinking of the coating, thesupport coated with the polyaddition silicone composition is placed at atemperature of greater than or equal to 110° C. preferably of between110 and 250° C. and more preferably still of between 130 and 170° C.,for less than 60 seconds, preferably less than 10 seconds.

Advantageously the silicone composition is a mixture formed of:

-   -   (I.1) at least one POS exhibiting, per molecule, at′ least two        alkenyl groups (preferably C₂-C₆ alkenyl groups) bonded to        silicon atoms,    -   (I.2) at least one crosslinking ≡Si—H POS as defined above,    -   (I.3) and/or at least one POS carrying Si-alkenyl and Si—H        units,    -   (II) at least one catalyst (II) composed of at least one metal        belonging to the platinum group.

Preferably, use is made of at least one POS (I.1) of Si-alkenyl type,for example Si-Vi type, and of at least one POS (I.2) of Si—H type.

The POS (I.1) is, by weight, one of the essential constituents of theformulation.

Advantageously, this POS (I.1) is a product comprising units of formula:$\begin{matrix}{W_{a}Z_{b}{SiO}\quad\frac{4 - \left( {a + b} \right)}{2}} & \left( {I{.1}} \right)\end{matrix}$in which:

-   -   W is an alkenyl group, preferably a vinyl or allyl group,    -   Z is a monovalent hydrocarbonaceous group which has no        unfavorable effect on the activity of the catalyst and which is        preferably chosen from alkyl groups having from 1 to 8 carbon        atoms inclusive, advantageously from the methyl, ethyl, propyl        and 3,3,3-trifluoropropyl groups, and also from aryl groups,        advantageously from the xylyl, tolyl and phenyl radicals,    -   a is 1 or 2, b is 0, 1 or 2 and a+b is between 1 and 3.

It is advantageous for this polydiorganosiloxane to have a viscosity (at25° C.) at least equal to 10 mPa·s, preferably between 50 and 1000mPa·s.

All viscosities concerned with in the present account correspond to adynamic viscosity quantity at 25° C. referred to as “newtonian”, that isto say the dynamic viscosity which is measured, in a way known per se,at a shear rate gradient which is sufficiently low for the viscositymeasured to be independent of the rate gradient.

The polyorganosiloxane (I.1) can exhibit a linear, branched or cyclicstructure. Its degree of polymerization is preferably between 2 and5000.

Examples of siloxyl units of formula (I.1) are the vinyldimethylsiloxaneunit, the vinylphenylmethylsiloxane unit and the vinylsiloxane unit.

Examples of polyorganosiloxanes (I.1) are dimethylpolysiloxanescomprising dimethylvinylsilyl ends, methylvinyldimethylpolysiloxanecopolymers comprising trimethylsilyl ends,methylvinyldimethylpolysiloxane copolymers comprising dimethylvinylsilylends, or cyclic methylvinylpolysiloxanes.

The crosslinking polyorganosiloxane (I.2) is preferably of the type ofthose comprising siloxyl units of formula: $\begin{matrix}{H_{d}L_{e}{SiO}\quad\frac{4 - \left( {d + e} \right)}{2}} & \left( {I{.2}} \right)\end{matrix}$in which:

-   -   L is a monovalent hydrocarbonaceous group which has no        unfavorable effect on the activity of the catalyst and which is        preferably chosen from alkyl groups having from 1 to 8 carbon        atoms inclusive, advantageously from the methyl, ethyl, propyl        and 3,3,3-trifluoropropyl groups, and from aryl groups,        advantageously from the xylyl, tolyl and phenyl radicals,    -   d is 1 or 2, e is 0, 1 or 2 and d+e has a value of between 1 and        3.

The dynamic viscosity η_(d) (at 25° C.) of this polyorganosiloxane (I.2)is ≧5, preferably ≧10, and more preferably still is between 20 and 1000mPa·s.

The polyorganosiloxane (I.2) can exhibit a linear, branched or cyclicstructure. The degree of polymerization is greater than or equal to 2.More generally, it is less than 5000.

Examples of units of formula (I.2) are: M′: H(CH₃)₂SiO_(1/2), D′:HCH₃SiO_(2/2), D′: H(C₆H₅)SiO_(2/2).

Examples of polyorganosiloxane (I.2) are:

-   -   M′DD′: dimethylpolysiloxanes comprising hydrodimethylsilyl ends,        poly(dimethylsiloxane)-(methylhydrosiloxyl)        α,ω-dimethylhydro-siloxane,    -   M′DD′: copolymers comprising dimethyl(hydro-methyl)polysiloxane        (dimethyl) units comprising trimethylsilyl ends,    -   M′DD′: copolymers comprising dimethyl-(hydromethyl)polysiloxane        units comprising hydrodimethylsilyl ends,    -   MD′: hydromethylpolysiloxanes comprising trimethylsilyl ends,    -   D′₄: cyclic hydromethylpolysiloxanes.

The polyaddition silicone composition bases may comprise only linearpolyorganosiloxanes (I.1) and (I.2), such as, for example, thosedisclosed in Patents: U.S. Pat. No. 3,220,972, U.S. Pat. No. 3,697,473and U.S. Pat. No. 4,340,709.

The catalysts (II) are also well known. Use is preferably made ofplatinum and rhodium compounds. It is possible in particular to use thecomplexes of platinum and of an organic product disclosed in PatentsU.S. Pat. No. 3,159,601, U.S. Pat. No. 3,159,602 and U.S. Pat. No.3,220,972 and European Patents EP-A-0 057 459, EP-A-0 188 978 and EP-A-0190 530, or the complexes of platinum and of vinylated organosiloxanesdisclosed in Patents U.S. Pat. No. 3,419,593, U.S. Pat. No. 3,715,334,U.S. Pat. No. 3,377,432 and U.S. Pat. No. 3,814,730. The catalystgenerally preferred is platinum. In this case, the amount by weight ofcatalyst (II), calculated as weight of platinum metal, is generallybetween 2 and 400 ppm, preferably between 5 and 200 ppm, based on thetotal weight of the polyorganosiloxanes (I.1) and (I.2).

Preferably, the crosslinking POS exhibits an ≡Si—H/≡Si-alkenyl (Vi)molar ratio such that:1.0≦≡Si—H/≡Si-alkenyl (Vi)≦4preferably1.4≦≡Si—H/≡Si-alkenyl (Vi)≦3.

It is advantageous for the POS (I.1) to be a blocked linearpolydiorganosiloxane comprising “Si-alkenyl” functional groups,preferably located at the chain end, exhibiting a viscosity of the orderof 100 to 1000 mPa·s and a level of alkenyl functional groups ¹a,expressed as equivalent number of alkenyl functional groups per 100 g ofoil, of:0.01≦1_(a)preferably0.015≦1_(a)≦0.04and more preferably still0.015≦1_(a)≦0.1.

Likewise, the oil of use as crosslinking agent comprising at least onePOS comprising ≡Si—H functional groups (I.2) exhibits, preferably, aviscosity of the order of 5 to 150 mPa·s.

The complete curable compositions are fluid at standard temperature;their viscosity is generally of the order of 50 to 500 mPa·s at 25° C.

According to an alternative form, the release crosslinkable siliconecomposition includes:

-   -   at least one adhesion-adjusting system (III);    -   and/or at least one agent for inhibiting hydrosilylation (IV),        preferably chosen from acetylenic alcohols and/or diallyl        maleates and their derivatives;    -   optionally at least one other additive chosen from bactericides        and/or antigelling agents and/or wetting agents and/or        antifoaming agents and/or fillers and/or synthetic latexes        and/or colorants and/or acidifying agents.

The adhesion-adjusting system (III) is selected from known systems. Itcan be those disclosed in French Patent FR-B-2 450 642, Patent US-B-3772 247 or European Patent Application EP-A-0 601 938. Mention may bemade, by way of examples, of the adjusting agents based:

-   -   on 96 to 85 parts by weight of at least one reactive        polyorganosiloxane resin (A) of type: MD^(Vi)Q, MM^(Vi)Q,        MD^(Vi)T, MM^(hexenyl)Q or MM^(allyloxyprobpyl)Q,    -   on 4 to 15 parts by weight of at least one nonreactive resin (B)        of type: MD′Q, MDD′Q, MDT′, MQ or MDQ.

The retardant of the addition reaction (IV) (crosslinking inhibitor)can, for its part, be chosen from the following compounds:

-   -   polyorganosiloxanes, advantageously cyclic polyorganosiloxanes,        which are substituted by at least one alkenyl,        tetramethylvinyltetrasiloxane being particularly preferred,    -   pyridine,    -   organic phosphines and phosphites,    -   unsaturated amides,    -   alkylated maleates,    -   and acetylenic alcohols.

These acetylenic alcohols (cf. FR-B-1 528 464 and FR-A-2372 874), whichare among the preferred thermal blockers for the hydrosilylationreaction, have the formula:R¹—(R²)C(OH)—C≡CHin which formula,R¹ is a linear or branched alkyl radical or a phenyl radical;R² is H, a linear or branched alkyl radical or a phenyl radical;it being possible for the R¹ and R² radicals and the carbon atomssituated a to the triple bond optionally to form a ring;the total number of carbon atoms present in R¹ and R² being at least 5,preferably from 9 to 20.

Said alcohols are preferably chosen from those exhibiting a boilingpoint of greater than 250° C. Mention may be made, by way of examples,of:

-   1-ethynyl-1-cyclohexanol;-   3-methyl-1-dodecyn-3-ol;-   3,7,11-trimethyl-1-dodecyn-3-ol;-   1, 1-diphenyl-2-propyn-1-ol;-   3-ethyl-6-ethyl-1-nonyn-3-ol;-   3-methyl-1-pentadecyn-3-ol.

These α-acetylenic alcohols are commercial products.

Such a retardant is present in a proportion of 3000 ppm at most,preferably in a proportion of 100 to 2000 ppm, with respect to the totalweight of the organopolysiloxanes (I.1) and (I.2).

According to another implementational route different from the“solvent-free” one, the composition is provided in the form of anaqueous emulsion/dispersion and then comprises at least one surfactantand optionally at least one agent for fixing the pH.

The agent for fixing and maintaining the pH is preferably a buffersystem comprising HCO₃ ⁻/CO₃ ²⁻ and/or H₂PO₄/HPO₄ ². Thus, in order toobtain the desired buffer effect, it will be advisable to introduce, inaccordance with the invention, an HCO₃ ⁻and/or H₂PO₄ salt, such as, forexample, NaHCO₃ and/or Na₂CO₃ and/or NaH₂PO₄ and/or Na₂HPO₄′. It isobvious that any other salt with a different counteranion (e.g. K) mightbe suitable. In a particularly preferred way, use is in practice made ofa buffer system composed of NaHCO₃ which is incorporated in theemulsion.

The surfactant or surfactants capable of being present in the emulsionaccording to the invention as emulsifying agent are nonionic or ionic innature.

According to an advantageous arrangement, the proportion of water in theemulsion is greater than or equal to 50% by weight, preferably greaterthan or equal to 55% by weight and, for example, in practice of theorder of 55-60% by weight or alternatively of 85 to 90% by weight.

According to another of its subject-matters, the invention relates to asilicone composition capable of crosslinking by polyaddition to form awater-repellent and release coating for a fibrous or nonfibrous support,characterized:

in that the composition comprises:

-   -   (I.1) at least one POS exhibiting, per molecule, at least two        alkenyl groups (preferably C₂-C₆ alkenyl groups) bonded to        silicon atoms,    -   (I.2) at least one silicone oil:        -   comprising at least one hydrogenated linear            PolyOrganoSiloxane (POS) exhibiting, per molecule, at least            three hydrogen atoms bonded to silicon atoms,        -   and having the following mean linear formula:            M_(α)M′_(β)D_(γ)D′_(δ)    -   with        -   M=(R¹)₃SiO_(1/2)        -   M′=H_(a)(R¹)_(b)SiO_(1/2), a+b=3, a=1, 2 or 3, b=0 to 3        -   D=(R²)₂SiO_(2/2)        -   D′=HR³SiO_(2/2)        -   0≦α≦2        -   0<β≦2        -   0<γ        -   0<δ    -   and with:    -   0<γ/δ≦0.4,    -   20≦(β/δ)×1000≦60,    -   at least one catalyst (II) composed of at least one metal        belonging to the platinum group; said catalyst being present at        a level of metal catalyst being of less than or equal to 80 ppm,        preferably of less than or equal to 65 ppm and more preferably        still of between 30 and 55 ppm;    -   and in that the POS or POSs of higher viscosity which it        comprises has (have) a dynamic viscosity η at 25° C. of less        than or equal to 1500 mPa·s.

To define the composition according to the invention, reference is madeto the characteristics defined above in the context of the descriptionof the use.

According to another of its aspects, the present invention relates to aprocess for the preparation of a silicone composition which can be usedin particular as coating base for the preparation of release andwater-repellent coatings, this composition being of the type of thatdefined above. According to this process, at least one (preferablylinear) ≡Si-Vi POS oil (I.1) is mixed with the crosslinking agentcomposed of at least one ≡Si—H POS oil (I.2) of MM′DD′ type and/or of amixture of oils comprising (preferably linear) POS molecules eachcarrying a portion of the MM′DD′ units present in the crosslinkingagent. The catalyst (II) is also incorporated in the silicone phase withthe optional other ingredients, such as the crosslinking inhibitors.

The mixing means and methodologies are known to a person skilled in theart, whether solvent-comprising, solvent-free or emulsion compositions.

These compositions can be applied using devices employed on industrialequipment for the coating of paper, such as a five-roll coating head, anair knife system or an equalizer bar system, to flexible supports ormaterials and can then be cured by moving through tunnel ovens heated to70-200° C.; the passage time in these ovens depends on the temperature;this time is generally of the order of 5 to 15 seconds at a temperatureof the order of 100° C. and of the order Of 1.5 to 3 seconds at atemperature of the order of 180° C.

Said compositions can be deposited on any flexible material orsubstrate, such as paper of various types (supercalendered, coated,glassine), board, cellulose sheets, metal sheets, plastic films(polyester, polyethylene, polypropylene, and the like), and the like.

The amounts of compositions deposited are of the order of 0.5 to 2 g perm² of surface to be treated, which corresponds to the deposition oflayers of the order of 0.5 to 2 μm.

The materials or supports thus coated can subsequently be brought intocontact with any pressure-sensitive adhesive material of rubber, acrylicor other nature. The adhesive material is then easily detachable fromsaid support or material.

According to another of its aspects, the present invention relates to asupport, characterized in that it comprises at least one release coatingobtained:

-   -   in accordance with the use as defined above,    -   and/or from a composition as defined above.

The following examples are given by way of indication and may not beregarded as a limitation on the scope and spirit of the invention.

EXAMPLES

1) Coating/Crosslinking of the silicone coating according to a specificmethodology M

The silicone composition is coated on a Rotomec pilot-scale coatingplant (while maintaining a residence time in the ovens of 1.8 s) on aglassine 9564 paper support, the Bekk smoothness of which is of theorder of 1020.

The temperature of the silicone layer is measured in-line using aninfrared camera. The temperature of the support is of the order of 150°C.

2). Characterization of the crosslinked silicone coating on the support

The coating, after coating and crosslinking, is characterized by thefollowing tests:

-   -   Weight of the silicone coating: the silicon atoms of the coating        are excited using a radioactive source or an X-ray fluorescence        tube and the X-ray intensity reemitted by the coating is        measured. The weight of the silicone coating is thus determined        using calibration. The device used is a Lab X1000 device sold by        Oxford.

Level of extractables (at the outlet of the coating device: in-line/4days after crosslinking: off-line): the test consists in immersing thecoating in toluene and in then quantitatively determining byPerkin-Elmer 3100 atomic absorption spectrophotometry (the siliconehaving transferred into the solvent). The level of silicone extractablefrom the coating is determined using calibration.

-   -   Crosslinking: the level of polymerization of the coating at the        outlet of the coating device is described using a number of        trade tests: the smear test, where the oily nature of the        surface is described by passing the finger over the silicone        surface.

The rub off test (Test. T), which characterizes the attachment to thesupport. In practice, the finger is rubbed over the surface of thecoating and the number of passes starting from which the coatingdeteriorates/detaches is recorded. A grading of 10 (10 passes) isregarded as acceptable for the application: POSITIVE ATTACHMENT.

-   -   Detachment force: the test used corresponds to the Finat No. 3        and 10 standards of edition No. 5 of 1999. This test is carried        out 4 days after crosslinking (off-line) with adhesive tapes        sold under the Tesa® 7475 trademark at 23° C. (acrylic base) and        the Tesa® 7476 trademark at 70° C. (rubber base).    -   Monitoring of the performance of pressure-free instantaneous        adhesion, tack, of the PSA after contact with the silicone        coating according to the No. 9 standard of the Finat edition No.        5 of 1999.        3) Products Used    -   Silicone oil vinylated in the chain and at the chain end (I.1):        vinylated PolyDiMethylSiloxane oil with 0.033 mol of Vi/100 g        and with a viscosity at 25° C.=230 mPa·s. This oil comprises        0.15% of EthylCycloHexanol inhibitor (IV).    -   Adjusting agent (III) which is a mixture of vinylated silicone        oil and of a vinylated MQ resin (50/50 mixture) comprising 0.107        Vi groups/100 g. This adjusting agent comprises 0.15% of ECH        inhibitor (IV).    -   Catalyst (II): Karstedt Pt comprising 2000 ppm of Pt.

Crosslinking agent (I.2) based on hydrogenated PDMS silicone oil or amixture thereof: the characteristics of these products are given in thefollowing table.

4) The Tests and Their Results

4.1 TESTS

Several hydrogenated silicone oils were tested comparatively. Thecharacteristics of these oils are given in the following table 1. TABLE1 Tests Structure γ/δ = D/D′ 1000 × β/δ = 1000 × M′/D′ 1M_(1.2)D₆D′₃₀M′_(0.8) 0.2 26.7 2 M_(0.8)D₄D′₂₅M′_(1.2) 0.16 48 3M_(1.3)D₁₇D′₃₃M′_(0.7) 0.52 21.2 4 M_(1.5)D_(13.7)D′₂₆M′_(0.5) 0.8 23 5M_(0.8)D₂₉D′₂₁M′_(1.2) 1.5 57.1 6 M_(1.4)D₂₁D′_(16.6)M′_(0.6) 1.25 35.77 M_(1.2)D′₃₀M′_(0.8) 0 26.7 8 M_(1.7)D₈D′₄₂M′_(0.3) 0.208 7.14 9M_(1.7)D_(10.5)D′_(33.4)M′_(0.3) 0.316 9 10 M_(1.6)D′₄₀M′_(0.4) 0 10 11M₁D₅D′₂₅M′₁ 0.2 40

These crosslinking agents are formulated with vinylated oil (I.1), theadjusting agent (I.3) and the catalyst (II).

The formulating rules followed are:

-   -   Si—H/Si-Vi ratio of 2.2    -   level of Pt in the final formulation: 60 ppm    -   level of adjusting agent of 40%.

4.2-FORMULAE TABLE 2 A B C D E F G H I J K Si—Vi oil 60 60 60 60 60 6060 60 60 60 60 (I.1) Adjusting 40 40 40 40 40 40 40 40 40 40 40 agent(III) Si—H 11.6 crosslinking agent (I.2), test 9 Si—H 10.7 crosslinkingagent (I.2), test 4 Si—H 18.2 crosslinking agent (I.2), test 6 Si—H 10crosslinking agent (I.2), test 8 Si—H 13.4 crosslinking agent (I.2),test 3 Si—H 21 crosslinking agent (I.2), test 5 Si—H 8.2 crosslinkingagent (I.2), test 7 Si—H 8.2 crosslinking agent (I.2), test 10 Si—H 10crosslinking agent (I.2), test 1 Si—H 10 crosslinking agent (I.2), test11 Si—H 10.2 crosslinking agent (I.2), test 2 Cata II 3.5 3.5 3.7 3.53.6 3.8 3.4 3.4 3.5 3.5 3.5

These formulations are coated on a glassine paper, ref 9564, with a Bekksmoothness of the order of 1020, from Ahlstrom; the weight of siliconedeposited is of the order of 1.2 g/m². The crosslinking conditions over1.8 s with a temperature of the coating of 150° C.

4.3-ATTACHMENT AND EXTRACTABLES EVALUATION

The performances in the rub off test and the level of extractables atthe oven outlet of the formulations evaluated have been combined in thefollowing table 3. It should be remembered here that the aim is to finda low level of extractables (sign of exhaustive polymerization) and goodbehavior in the rub off test. TABLE 3 Tests Structure γ/δ = D/D′ 1000 ×β/δ = 1000 × M′/D′ Attachment Extractables 1 InventionM_(1.2)D₆D′₃₀M′_(0.8) 0.2 26.7 YES 6.50% 2 InventionM_(0.8)D₄D′₂₅M′_(1.2) 0.16 48 YES 5.80% 3 ComparativeM_(1.3)D₁₇D′₃₃M′_(0.7) 0.52 21.2 NO 4.40% 4 ComparativeM_(1.5)D_(13.7)D′₂₆M′_(0.5) 0.8 23 NO 4.00% 5 ComparativeM_(0.8)D₂₉D′₂₁M′_(1.2) 1.5 57.1 NO 3.40% 6 ComparativeM_(1.4)D₂₁D′_(16.6)M′_(0.6) 1.25 35.7 NO 3.20% 7 ComparativeM_(1.2)D′₃₀M′_(0.8) 0 26.7 YES 11.10% 8 ComparativeM_(1.7)D₈D′₄₂M′_(0.3) 0.208 7.14 YES 10.00% 9 ComparativeM_(1.7)D_(10.5)D′_(33.4)M′_(0.3) 0.316 9 YES 9.90% 10 ComparativeM_(1.6)D′₄₀M′_(0.4) 0 10 YES 9.10% 11 Invention M₁D₅D′₂₅M′₁ 0.2 40 YES6.20%

It is clearly seen that the crosslinking agents (1.2) according to theinvention with the ≡Si—H POS structure M'MD'D (tests 1, 2 and 11) makeit possible to obtain the lowest levels of extractables, the mark ofbetter reactivity, with good attachment to the support. By virtue of theinvention, formulations are accessible which can be crosslinked at a lowlevel of Pt.

1. A crosslinking agent (I.2), for use in a silicone composition capableof crosslinking by polyaddition in the presence of a metal catalyst toform a water-repellent and release coating for a fibrous or nonfibroussupport, of at least one silicone oil comprising at least onehydrogenated (optionally linear) PolyOrganoSiloxane (POS) exhibiting,per molecule, at least three hydrogen atoms bonded to silicon atoms, andhaving the following mean formula:M_(α)M'_(α)D_(γ)D_(δ) with M=(R¹)₃SiO_(1/2) M′=H_(a)(R¹)_(b)SiO_(1/2),a+b=3, a=1, 2 or 3, b=0 to 3 D=(R²)₂SiO_(2/2) D′=HR³SiO_(2/2) 0≦α≦20<β≦2 0<γ 0<δ and with: 0<γ/δ≦0.4, 20≦(β/δ)×1000≦60, the POS or POSs ofhigher viscosity of said composition having a dynamic viscosity η at 25°C. of less than or equal to 1500 mPa·s; the level of metal catalystbeing less than or equal to 80 ppm.
 2. The use crosslinking agent asclaimed in claim 1, wherein the silicone composition is such that it canbe converted according to a specific methodology M to a crosslinkedsilicone elastomer coating on a support made of paper with a Bekksmoothness of greater than 1000, said coating having a positiveattachment in a specific test T.
 3. The use crosslinking agent asclaimed in claim 1 wherein the support intended to be coated is made ofa heat-sensitive material, optionally selected from flexible supportsmade of paper, board or the like, flexible supports composed of theadhesive face of a label or of a tape of the same kind, woven ornonwoven fibrous flexible supports, flexible supports comprisingpolyethylene and/or polypropylene and/or polyester and/or poly(vinylchloride), and/or thermally printable flexible supports.
 4. Thecrosslinking agent as claimed in claim 1, wherein, for the crosslinkingof the coating, the support is placed at a temperature of less than orequal to 110° C., for less than 60 seconds.
 5. The crosslinking agent asclaimed in claim 1, wherein the silicone composition is a mixture formedof: (I.1) at least one ≡Si-alkenyl POS exhibiting, per molecule, atleast two alkenyl groups bonded to silicon atoms, (1.2) at least onecrosslinking ≡Si—H POS as defined above, (1.3) and/or at least one POScarrying Si-alkenyl and Si—H units, (II) at least one catalyst (II)comprising at least one metal belonging to the platinum group.
 6. Thecrosslinking agent as claimed in claim 5, wherein the crosslinking POSexhibits an ≡Si—H/≡Si-alkenyl (Vi) molar ratio such that:1.0≦≡Si—H/≡Si-alkenyl(Vi)≦4.
 7. The crosslinking agent as claimed inclaim 6, wherein the POS (I.1) is a product comprising units of formula:$\begin{matrix}{W_{a}Z_{b}{SiO}\quad\frac{4 - \left( {a + b} \right)}{2}} & \left( {I{.1}} \right)\end{matrix}$ in which: W is an alkenyl group, Z is a monovalenthydrocarbonaceous group which has no unfavorable effect on the activityof the catalyst and which is selected from alkyl groups having from 1 to8 carbon atoms inclusive, optionally from the methyl, ethyl, propyl and3,3,3-trifluoropropyl groups, and also from aryl groups, optionally fromthe xylyl, tolyl and phenyl radicals, a is 1 or 2, b is 0, 1 or 2 anda+b is between 1 and
 3. 8. The crosslinking agent as claimed in claim 1,wherein the release crosslinkable silicone composition comprises: atleast one adhesion-adjusting system (III), and/or at least one agent forinhibiting hydrosilylation (IV).
 9. The crosslinking agent as claimed inclaim 1, wherein the POS (I.1) is a blocked linear polydiorganosiloxanecomprising “Si-alkenyl” functional groups, exhibiting a viscosity of theorder of 100 to 1000 mPa·s and a level of alkenyl functional groupsI_(a), expressed as equivalent number of alkenyl functional groups per100 g of oil, of:0.010≦1_(a.)
 10. The crosslinking agent as claimed in claim 1, whereinthe oil of use as crosslinking agent comprising at least one POScomprising ≡Si—H functional groups (I.2) exhibits a viscosity of theorder of 5 to 150 mPa·s.
 11. The crosslinking agent as claimed in claim1, wherein the composition is provided in the form of an aqueousemulsion/dispersion.
 12. A silicone composition capable of crosslinkingby polyaddition to form a water-repellent and release coating for afibrous or nonfibrous support, wherein: in that the compositioncomprises: (I.1) at least one POS exhibiting, per molecule, at least twoalkenyl groups bonded to silicon atoms, (I.2) at least one silicone oil:comprising at least one hydrogenated linear PolyOrganoSiloxane (POS)exhibiting, per molecule, at least three hydrogen atoms bonded tosilicon atoms, and having the following mean linear formula:M_(α)M′_(β)D_(γ)D′_(δ) with M=(R¹)₃SiO_(1/2) M′=H_(a)(R¹)_(b)SiO_(1/2),a+b=3, a=1, 2 or 3, b=0 to 3 D=(R²)₂SiO_(2/2) D′=HR³SiO_(2/2) 0≦α≦20<β≦2 0<γ 0<δ and with: 0<γ/δ≦0.4, 20≦(β/δ)×1000≦60, at least onecatalyst (II) comprising at least one metal belonging to the platinumgroup; said catalyst being present at a level of metal catalyst being ofless than or equal to 80 ppm; and in that the POS or POSs of higherviscosity which it comprises has (have) a dynamic viscosity 1n at 25° C.of less than or equal to 1500 mPas.
 13. A composition prepared using thecrosslinking agent as claims in claim
 1. 14. A support comprising atleast one release coating obtained: using the crosslinking agent asclaimed in claim 1.